code: def data():
      """Generates test dataframe for outlier detection"""
      np.random.seed(100)
      df = pd.DataFrame(
          {
              "a": np.repeat(1.0, 100),
              "b": np.arange(0.0, 100.0, 1.0)
              + np.random.normal(size=100, loc=0, scale=0.1),
              "c": np.tile([1.0, 2.0, 3.0, 4.0], 25),
              "d": np.repeat(1.0, 100),
          }
      )
      df.loc[2, "b"] = 100.0
      df.loc[6, "d"] = 100.0
      return df
  
file_path: greykite/greykite/tests/sklearn/transform/test_difference_based_outlier_transformer.py
imports: import numpy
  import pandas
  import pytest
  from sklearn.exceptions import NotFittedError
  from testfixtures import LogCapture
  from greykite.common.constants import LOGGER_NAME
  from greykite.common.python_utils import assert_equal
  from greykite.sklearn.transform.difference_based_outlier_transformer import DifferenceBasedOutlierTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: data() and returns: df